1. Field of the Invention
The present invention relates to a method for diagnosing the availability of network subscribers in an IP-based network, in which each of the network subscribers can be allocated, in one or more address ranges, at least one respective address at which the relevant network subscriber is available to another network subscriber. The invention additionally relates to a network subscriber carrying out the method, and to an IP-based network, particularly an IPv6-based network.
2. Background of the Invention
In IPv6-based networks, a plurality of addresses in a plurality of address ranges (what are known as address levels) may be in use simultaneously by a single network subscriber. This is used in practice particularly in smaller industrial automation networks with access to the internet. Typically, four address ranges are then simultaneously in use, namely one LLA (Link-Local Address), one ULA (Unique Local Address) and two GUAs (Global Unicast Addresses). In the field of industrial automation networks, for example, but also in other applications, the simultaneous use of a plurality of address ranges accommodates separate addresses for IT components and for automation components. By way of illustration, for IT components, global addresses for service activities can be provided from outside the automation network, whereas the addresses allocated to automation can be viewed and administered without IT planning operations. Thus, automation addresses can be used and administered autonomously, i.e. without use or inspection by IT experts. Networks of this type are currently structured such that it is possible to access addresses reserved for automation only on site; remote maintenance from locations outside of the network is not possible.
In principle, however, it would be desirable if, in the future, additional addresses or address ranges could be temporarily activated, for example for remote services, so as to thereby allow external network subscribers intermittent access to a restricted number of network subscribers, such as automation devices.
The fundamental availability of network subscribers, such as automation components, in an IPv4-based network is determined with a diagnosis tool that uses what are known as pings. If the ping is successful, the device is deemed to be fundamentally available. However, IP networks regularly involve the use of just one address range, which means that it is relatively easy to check whether two network subscribers can communicate with one another. To this end, a further network subscriber, such as a diagnosis computer, checks the availability of each network subscriber individually using pings. From a technical point of view, this is accomplished by using what are known as ICMP Echo messages. If the diagnosis computer reaches the network subscribers, then they are considered to also be able to communicate with one another in the IPv4 network.
This rigid and straightforward conclusion is normally not valid in IPv6 networks. This is because, in order to communicate with another network subscriber, it is necessary for a network subscriber to make a selection as between the available addresses of the two network subscribers. This choice is additionally influenced by the guidelines that are locally maintained on the network subscribers, which are for the most part advantageously of the same type for all of the network subscribers within a network. However, configuration errors or local requirements may mean that these guidelines may also differ.
The result of this is that, when the availability of network subscribers is investigated or determined in the manner described above in an IPv6 network by the diagnosis computer, the two network subscribers may in fact be perfectly available. Nevertheless, the connection setup and hence the communication between the network subscribers may be disrupted, since there is no check on the actual communication path between the network subscribers or on the guidelines that are stored on the respective network subscribers. Yet the applications installed on the network subscribers must observe these ancillary conditions.
The check on the actual communication path between the two network subscribers requires a technical facility in situ, i.e. the diagnosis computer must be connected to at least one of the two network subscribers directly for checking purposes. Owing to the often long distances between the individual network subscribers in an industrial automation network, this is normally not feasible. However, even if the diagnosis computer is available in situ, in order to determine the availability of another network subscriber from one network subscriber, difficulties from the problems described above cannot be totally ruled out.
By way of example, pings can be used to check the address in a first address range and to confirm it to be correct. If the local guidelines are not taken into consideration, however, the result of that check is incomplete, which may lead to problems in the communication sequence.